1. Field of the Invention
Factor IX (Christmas factor) is a vitamin K-dependent plasma protein that plays an important role in the middle phase of blood coagulation. Individuals lacking this protein may bleed spontaneously into their skin, soft tissues and joints. This bleeding is often serious in patients even after a minor injury. A deficiency of factor IX (Christmas disease or hemophilia B) affects males primarily, since it is transmitted as a sex-linked recessive trait. The human and bovine proteins contain 12 .gamma.-carboxyglutamic acid residues in their amino-terminal regions. During the coagulation process, factor IX is converted to factor IX.sub.a (a serine protease) by factor XI.sub.a, Fujikawa et al., Biochemistry (1974) 13:4508-4516. This factor then reacts with factor X and by successive steps coagulation occurs.
The amount of factor IX is extremely small and only difficultly obtainable. There is, therefore, difficulty in either obtaining the genetic information from the chromosome or preparing sufficient messenger RNA for successful reverse transcription of a complete sequence for factor IX.
2. Description of the Prior Art
Factor IX has been extensively purified from bovine and human plasma, as described by Fujikawa et al., Biochemistry (1973) 12:4938-4945 and DiScipio et al., ibid. (1977) 16:698-706. Approximately 20% of the amino acid sequence for the human molecule has been determined, DiScipio et al., J. Clin. Invest. (1978) 61:1528-1538. The entire sequence for the bovine molecule has been established. Katayama et al., PNAS USA (1979) 76:4990-4994. Both proteins are single-chain glycoproteins (M.sub.r, 55,000- 57,000) with an amino-terminal sequence of Y-N-S-G-K. Choo et al., Nature (1982) 299:178-180, describe the partial characterization of the human factor IX gene.